In a Time Division Duplex (TDD) system, uplink transmission and downlink transmission can use the same frequency resources and different time resources, that is, uplink data and downlink data is transmitted in different sub-frames. In common TDD systems including a Time Division-Synchronous Code Division Multiple Access (TD-SCDMA) system and a Time Division-Long Term Evolution (TD-LTE) system, the partitions of uplink sub-frames and downlink sub-frames are statically or semi-statically, and it is common to determine a partition scheme of uplink and downlink sub-frames during a network planning according to the type of a cell and a rough proportion of traffic and keep the partition scheme unchanged. This is a simple and effective method in the context of large coverage by a macro cell. However an increasing number of low-power base stations including a pico cell, a home NodeB, etc., have been used to provide small local coverage along with the advancement of technologies, and there are a smaller number of User Equipments (UEs) and a significant change in UE's traffic requirements in these cells, thus the configuration of uplink sub-frames and downlink sub-frames is needed to varied dynamically as needed. Moreover inter-cell interference across uplink and downlink time slots may be obviated by synchronization and the same configuration of uplink and downlink sub-frames throughout the traditional TDD network, and particularly if an adjacent cell uses a sub-frame for an uplink transmission, then a current cell can't use this sub-frame for the downlink transmission but only can set this sub-frame as an uplink sub-frame or idle. Due to different conditions of traffic in the respective cells, the operation of the real network may be greatly restricted due to this traditional practice in that the respective cells can't select the configuration scheme of uplink sub-frames and downlink sub-frames dependent upon their own real-time conditions of traffic, thus lowering the ratio of utilizing system resources of the TDD network.
In view of the problem above, some more flexible configuration solutions of uplink and downlink sub-frames have gain attention, and in such solutions, a cell in the TDD network can select a different configuration scheme of uplink and downlink sub-frames as needed, and can adapt flexibly the configuration scheme of uplink and downlink sub-frames in accordance with a dynamic change in traffic to thereby improve the ratio of utilizing system resources.
A frame structure of the TD-LTE system in the prior art is as illustrated in FIG. 1, where the length of a radio frame is 10 ms, which includes 10 sub-frames, each of which is 1 ms in length. The sub-frames in the radio frame include special sub-frames and normal sub-frames, where the normal sub-frames include uplink sub-frames and downlink sub-frames for transmitting uplink/downlink control signaling, traffic data, etc., and the special sub-frames each include three time slots, which are a Downlink Pilot Time Slot (DwPTS), a GP and an Uplink Pilot Time Slot (UpPTS), the DwPTS being for transmitting a Primary Synchronized Signal (PSS), a Physical Downlink Control Channel (PDCCH), a Physical Hybrid Automatic Repeat Request (HARQ) Indication Channel (PHICH), a Physical Control Format Indication Channel (PCFICH), a Physical Downlink Shared Channel (PDSCH), etc., the GP being a guard period between the downlink and the uplink, and the UpPTS being for transmitting a Sounding Reference Signal (SRS), a Physical Random Access Channel (PRACH), etc. Particularly a radio frame can be configured with two special sub-frames (the sub-frames #1 and #6) or can be configured with a special sub-frame (the sub-frame #1), and the sub-frame #0 and the sub-frame #5, and the DwPTS time slot(s) in the special sub-frame(s) are usually used for downlink transmission, the sub-frame #2 and the UpPTS time slot(s) in the sub-frame(s) are usually used for uplink transmission, and the remaining sub-frames can be configured for uplink transmission or downlink transmission as needed.
In the TD-LTE system, the lengths of three time slots DwPTS, GP and UpPTS in a special sub-frame are allocated to support different configuration conditions, as depicted in Table 1:
TABLE 1ConfigurationNormal CPExtended CPNo.DwPTSGPUpPTSDwPTSGPUpPTS0 6592 · Ts21936 · Ts 2192 · Ts 7680 · Ts20480 · Ts 2560 · Ts119760 · Ts8768 · Ts20480 · Ts7680 · Ts221952 · Ts6576 · Ts23040 · Ts5120 · Ts324144 · Ts4384 · Ts25600 · Ts2560 · Ts426336 · Ts2192 · Ts 7680 · Ts17920 · Ts 5120 · Ts5 6592 · Ts19744 · Ts 4384 · Ts20480 · Ts5120 · Ts619760 · Ts6576 · Ts23040 · Ts2560 · Ts721952 · Ts4384 · Ts———824144 · Ts2192 · Ts———
In Table 1, the length unit is Ts, where Ts=1/(15000×2048) second. In the existing TD-LTE system, seven different allocation schemes of uplink and downlink sub-frames are supported with their particular configuration parameters as depicted in Table 2, where D represents downlink transmission, U represents uplink transmission, and S represents that this sub-frame is a special sub-frame:
TABLE 2Configura-SwitchSub-frame indextion No.periodicity012345678905 msDSUUUDSUUU15 msDSUUDDSUUD25 msDSUDDDSUDD310 ms DSUUUDDDDD410 ms DSUUDDDDDD510 ms DSUDDDDDDD65 msDSUUUDSUUD
Where the configuration scheme of sub-frames is broadcasted by the network side to all of UEs in a cell in System Information (SI), and a change to the configuration scheme of sub-frames by using a modification to the system information is supported in the TD-LTE standard, but this modification necessitates procedures of paging, reading the system information again, etc., and the performance of the system may be degraded seriously if the configuration scheme of sub-frames is changed frequently. Moreover the shortest modification periodicity of frame configuration of 640 ms is supported in the TD-LTE standard, which has failed to fully accommodate a dynamically varying requirement for traffic.
In view of this, a more flexible TDD frame structure has been proposed in the prior art to support more dynamic reconfiguration of uplink and downlink sub-frames so as to accommodate dynamically varying traffic. Particularly in a specific period of time, four types of sub-frames are set, including sub-frames always used for downlink transmission (referred to as constant downlink sub-frames), sub-frames always used for uplink transmission (referred to as fixed uplink sub-frames), special sub-frames, and sub-frames flexibly allocated for uplink or downlink transmission, where the sub-frames flexibly allocated for uplink or downlink transmission are referred to as flexible sub-frames, and if a flexible sub-frame is used for uplink transmission, then the flexible sub-frame is referred to as a flexible uplink sub-frame, or if a flexible sub-frame is used for downlink transmission, then the flexible sub-frame is referred to as a flexible downlink sub-frame. As illustrated in FIG. 2, the period of time above is a radio frame, where the sub-frames #0 and #5 are fixed downlink sub-frames, the sub-frames #2 and #7 are fixed uplink sub-frames, the sub-frames #1 and #6 are special sub-frames, and the remaining sub-frames (the sub-frame #3, the sub-frame #4, the sub-frame #8 and the sub-frame #9) are flexible sub-frames. The flexible sub-frames can be configured dynamically by the base station in view of a real-time traffic demand and a real-time channel condition to accommodate a dynamic change in traffic demand.
In the flexible configuration solution above of uplink and downlink sub-frames, although uplink and downlink sub-frames may be configured flexibly to dynamically varying traffic, serious interference across timeslots may arise, including interference between base stations and interference between UEs, as illustrated in FIG. 3, where an M-UE represents a UE served by a macro base station, and an L-UE represents a UE served by a home base station. A study showed that interference with a larger influence upon the performance of the system is interference between base stations, that is, uplink reception by a current base station may be subject to interference of downlink transmission by an adjacent base station, so that the performance of uplink transmission by a UE served by the current base station may be deteriorated seriously.
Uplink power can be controlled to improve the performance of uplink transmission. Wherein the power control as a fundamental technology in a wireless communication system serves to compensate for an influence of fading over a radio channel, so that a signal can arrive at a receiver at appropriate power in such a way that transmit power can be lowered at a transmitter when there is a good condition of the channel and can be increased at the transmitter when there is a poor condition of the channel to thereby guarantee the performance of reception so that a signal to noise ratio at the receiver is maintained in a relatively constant range. With a reasonable power control scheme, power consumption at the transmitter can be lowered on one hand and interference between UEs in a cell can be avoided on the other hand to thereby improve the performance of transmission and the capacity of the system. Moreover mutual interference between cells can be controlled. General power control schemes can include open-loop power control, closed-loop power control, inner-loop power control, outer-loop power control, etc. Uplink power is controlled in the LTE system by open-loop estimation in combination with closed-loop adjustment, where the open-loop section involves determination of an initial value of uplink transmit power by a UE from an uplink power control parameter (e.g., a target value of received power) configured at the network side, and then real-time closed-loop adjustment is performed on uplink transmit power in response to a power control command issued by a base station.
In the traditional TD-LTE system with synchronization and the same configuration scheme of uplink and downlink sub-frames throughout the network, there will be no interference across time slots, and uplink transmission by a cell will be subjected only to interference of uplink transmission in an adjacent cell, so an uplink power control parameter, which is determined by the deployment of the network, will be applicable to all the uplink and downlink sub-frames. There are two types of uplink sub-frames in the dynamic TDD system, which include fixed uplink sub-frames and those sub-frames among flexible sub-frames allocated for uplink transmission (i.e., flexible uplink sub-frames). There may be different interference conditions in these two types of uplink sub-frames, where the interference condition in the first type of uplink sub-frames is the same as that in the traditional TD-LTE system because a current cell will be subjected only to interference of uplink transmission of an adjacent cell; and in the second type of uplink sub-frames uplink transmission of the current cell may be subjected to persistent interference of downlink transmission of the adjacent cell at a significantly higher interference level than that in the first type of uplink sub-frames, and moreover since uplink or downlink transmission is performed flexibly by the adjacent cell in the respective ones of the second type of uplink sub-frames, there may also be significantly different interference conditions between the respective sub-frames.
As can be apparent from the description above, there may be greatly varying transmit power of the UE required in the respective types of uplink sub-frames in the dynamic TDD system. In order to guarantee the performance of transmission by the UE in the respective types of uplink sub-frames in the dynamic TDD system, transmit power in the different uplink sub-frames can be adjusted by a power control command word, but a narrow dynamic range of the power control command word, typically within ±2 dB, may not satisfy the requirement; and moreover respective UEs can be particularly configured with a uniform uplink power control parameter corresponding to transmit power, which results in unnecessary power consumption by the UEs and inter-cell interference in some other sub-frames (e.g., downlink sub-frames). Thus uplink transmit power can not be controlled flexibly without power consumption and interference in the prior art.